1. Field of the Invention
The present invention relates to a bicycle caliper brake assembly, and more particularly to a caliper brake assembly of the type which has a completely concealed return spring system to prevent rusting, by the rain water, of the spring system in addition to providing attractive appearance and improved aerodynamic characteristics.
2. Description of the Prior Art
As is well known, a side-pull type caliper brake assembly, which is most commonly used in current bicycles, comprises a pair of brake calipers pivotally supported on a support shaft and always urged by a return spring to pivot away from each other. Conventionally, such a return spring is exposed to the exterior, so that it is subjected to the adverse influences of the rain water, mud, dust, and so on. Further, the exposed return spring deteriorates the visual attractiveness and aerodynamic characteristics of the overall brake assembly.
In order to avoid these drawbacks of the exposed return spring, Japanese Utility Model Application Laid-open No. 60-136283 (Laid-open: Sept. 10, 1985; Appln. No. 59-24698; Filed: Feb. 22, 1984; Applicant: Shimano Industrial Co. Ltd.; Inventor: Masashi NAGANO) proposes an improved caliper brake assembly employing a completely concealed or enclosed return spring system. More specifically, the brake assembly of this laid-open application comprises first and second calipers respectively having bosses rotatably fitted on a support shaft as interposed between an intermediate flange of the shaft and a double nut adjustably screwed on the shaft. An engaging disk is non-rotatably fitted on the support shaft between the first and second calipers. Both calipers are biased to pivot away from each other by first and second coil springs respectively accommodated within the bosses of the first and second calipers. The second spring has one end directly engaging the boss of the second caliper and the other end caught by the engaging disk. Thus, the second caliper is always under the influence of the second spring. The brake assembly further includes an operating member which is especially provided for initial energization of the first spring.
The operating member comprises a headed sleeve rotatably fitted on the support shaft and rotatably penetrating through the boss of the first caliper to project outward therefrom toward the intermediate flange of the support shaft with the head of the sleeve positioned within the first caliper boss. The operating member further includes a lever co-rotatably fitted on the projecting end of the sleeve. The first spring has one end engaging the head of the sleeve and the other end arrested by the engaging disk. The lever of the operating member is forcibly pivoted to initially torsion the first spring and subsequently bolted to a predetermined portion of the first caliper boss to bring the first caliper under the influence of the first spring.
As described above, the prior art brake assembly requires the specially devised operating member for initial energization of the first spring. This is because one of the two calipers has a projecting portion (e.g. shoe support portion) which comes into abutment with a functional portion (e.g. connecting portion for connection to a control cable) of the other caliper, thereby preventing both calipers to pivot away from each other to their preparatory position for initial torsional energization of the spring. Thus, it becomes necessary to employ some means which enables initial energization of the spring irrespective of the relative position between the two calipers.
Naturally, the operating member of the prior art brake assembly is an additional component which is used only for initial energization of the first spring but cannot be removed even after such energization, consequently complicating the overall structure of the assembly. Further, subsequent bolting, to the first caliper boss, of the lever of the operating member necessitates exact positional adjustment between the lever and the boss and thereby requires a lot of skill.